The present invention is related generally to a new and improved apparatus for photographic printing and is more particularly concerned with a novel apparatus for photographically exposing a photoresist layer on a semiconductor wafer by a scanning technique.
Modern technology is relying to an increasing extent on the use of integrated circuit components for performing a multitude of functions previously performed, if at all, by discrete circuit components. Therefore, the demand is increasing for new and improved techniques and apparatus for producing such integrated circuit components with greater reliability and at a lesser cost.
Conventionally, integrated circuit components have been produced by exposing a photoresist layer which has been deposited on a semiconductor wafer such that it records faithfully the image of a master mask on that semiconductor wafer. The image recorded in the photoresist layer is then utilized to form the various component elements of the integrated circuits by techniques which are well known in the art and which do not form a part of the present invention.
One such technique which has been widely utilized for exposing the photoresist layer is contact printing. In contact printing, the master mask is pressed into physical contact with the photoresist layer and an exposure of the photoresist is then made. A major difficulty has occurred with the utilization of this technique in that, after a number of printing operations have been made with a mask, imperfections in the semiconductor surface and photoresist layer tend to damage the mask thereby making its useful life only a few cycles. A new mask must then be substituted which leads to significantly increased costs and time during the manufacturing process.
One method which has been derived which overcomes the problems of wear damage to the mask is to projection print the information contained in the master mask into the photoresist layer with an optical system. To be a viable process, resolution exceeding one micrometer line width in the projected image must be attained. To accomplish such resolution, the optical system must be large, expensive and be constructed to extremely critical tolerances. Furthermore, the larger the area which must be transferred from the mask to the semiconductor wafer, the more difficult and complex the lens design becomes. In addition, problems exist in projection printing techniques with regard to focussing the image on the semiconductor material and in maintaining registration with previously imposed images. Necessarily, all of these problems lead to significant increases in cost and complexity of the apparatus utilized for forming the integrated circuit.